1. Field of the Invention
This invention relates to an engine control device for controlling an engine and, more specifically to an engine control device suitable for controlling an engine provided with a fuel injection device for injecting fuel.
2. Description of the Related Art
With the widespread use of fuel injection devices called injectors in recent years, control of fuel injection timing and fuel injection amount, namely, the air-fuel ratio, has become easy, which makes it possible to improve engine output and fuel consumption and to clean exhaust gas. As to the fuel injection timing, the phase state of a camshaft, that is the state of an intake valve, is commonly detected, and fuel injected based on the detected result. However, it is difficult to employ a cam sensor to detect the phase state of a camshaft, particularly in motorcycles, because it is expensive and increases the size of a cylinder head. To solve this problem, an engine control device adapted to detect the phase state of a crankshaft and an intake air pressure is proposed in JP-A-H10-227252. Based on the detection of the phase state and air intake pressure, the engine control device detects the stroke state of a cylinder. It is thus possible to detect the stroke state of a cylinder without detecting the phase of a camshaft, so that it is possible to control fuel injection timing based on the stroke state.
For example, the phase of a crankshaft is detected as follows. The crankshaft, or a member which is rotated in synchronization with the crankshaft, has teeth formed on an outer periphery thereof at equal intervals with an irregular interval part. Crank pulses are generated by a crank pulse generating means, such as a magnetic sensor, with the rotational movement of the teeth. A specific rotational position of the crankshaft corresponding to the irregular interval part of the teeth is detected based on the state of the crank pulses. The rotational angle, namely the phase, of the crankshaft can be detected based on, for example, the number of the crank pulses from the specific rotational position of the crankshaft. However, when the positional relation between the crank pulse generating means, such as a magnetic sensor, and the teeth is not appropriate, the crank pulses may not be properly generated. Crank pulses generated by crank pulse generating means, such as a magnetic sensor, are obtained by converting a current continuously varying as a sine curve into binary ON-OFF signals with a prescribed value. Thus, when the sensor is too close to the teeth, the pulses become long or no OFF-part is generated, and when the sensor is too far apart from the teeth, the pulses become short or no ON-part is generated. In addition, there is no specific conventional method for detecting an abnormal condition of the crank pulse generating means.
The present invention has been made to solve the above problems and it is, therefore, an object of the present invention to provide an engine control device which can reliably detect an abnormal condition of crank pulse generating means.